brake actuator resistor

My mechanic replaced the actuator assembly due to its continuously turning on every 30 sec for 2 sec. The new actuator hardly ever turn on. The brake feels more firm, probably due to bleeding the brake as part of the actuator replacement task. The associated resistor in the dash was accessed from below with some difficulty.

 

I would be very interested to hear what happens when one of these actuators gets powered up on the bench, using different values for the resistor. For that matter, could someone check the value of those resistors to see how they vary? The resistor is in series with the 12V supply, so acts as a current limiter. The manual says that the pump motor and resistor need to be replaced together because pump noise may be increased. If the resistor is difficult to access, and the need for replacement is conditional, it would be good to know what the parameters are.

 

I noticed the new actuator pump will come on for 2 seconds every time after 3 or 4 gentle press of brake, either while driving or in park. Is this normal, or indicative of other issues?

 

I used a private mechanic specialized in Toyota. They only use Toyota parts for all of the repairs. Do not know the particular tool used. I know they use a labtop PC connected to the Toyota server.

 

Normal. The pro's use Techstream from Toyota to do the brakes. Most DIY's use the "mini VCI" for this.

 

Is this a picture of the old actuator and new resistor? If so, I'm pretty sure both resistors are the same value.

 

The value of 193.6 milli-ohm is interesting. That is a very precise spec for a resistor. With all the heat fins, it would look to be something like 25-50 watts. If so, I would guess about 10-15A of current flow through it @ 12V. I find it hard to imagine what would be the requirement for such precision in a DC motor. In theory, it should be possible to measure the old resistor, and determine if it is indeed necessary to replace it when replacing the pump. In practice, it takes some doing to measure low values with accuracy. OTOH that is a pretty simple plug fitting, which will have it's own small variation in resistance, especially over time, so again the precision does not make sense.

 

If replacing the brake actuator becomes necessary as a DIY project, I would leave the old resistor in and not worry about it. There does not appear to be any issue with safety or functionality - only the potential for more noise produced by the actuator motor.

 

There are instructions that say replacing the resistor is not required but may cause noise if not replaced.

 

Avi

Do you notice on the 2nd Gens you work on, the 2008 and 2009 actuators make less noise? Much quieter than the 2007 and under cars? I notice that with my 2006 making a louder sound. I don't know why the newer cars would be better insulated from noise......or possibly I have a bummed 2006 actuator

 

Okay, I'm taking my prius apart to replace the attenuator and I was wondering, with they safety plug pulled and the 12v battery disconnected, does the power unit under the hood hold electricity? I have disconnected the plug on the firewall side and the plug on the front bumper side but haven't taken the screws out inside the unit, do they have voltage on them? Don't won't to be shocked.

 

What is the "attenuator"? Do you mean the brake actuator assembly?

In any event, if you need to remove the inverter for access, you are supposed to use a multimeter to measure voltage at the high voltage battery cables before disconnecting them. Make sure the voltage across the cables; and voltage from each cable to ground is zero. The purpose of doing that is to make sure that the capacitors in the inverter have discharged.

Also, even if you have removed the orange safety interlock at the traction battery, it is still possible for high voltage to be present if the battery has a ground fault and if a system main relay is stuck closed.

 

Yes that is what I meant. I will check the bolts inside the inverter before I go any further. If there is a charge, what is the best way to drain it off so I can safely work with it?

 

There shouldn't be a voltage reading if you've waited more than a few minutes after the car was made IG-OFF.

In the unlikely event there is a charge, you would need to apply a resistor across the battery cables to discharge the capacitors. Hopefully that will not become an issue - because if it is, you would need to determine a suitable resistance value and power handling capacity of the resistor, etc.

 

I just noticed this question! No, I never noticed that, but I will pay attention to it from now on. Sorry for the late reply.

 

If you want to remove the dash top to get access to the resistor the first 8 1/2 minutes of this video will be useful.

 

I discovered you don't have to take the dash apart to replace this resistor (44535-47050). You can do it from underneath the dash if you are somewhat flexible.

First put your seat back all the way, then wriggle underneath the dash and look up and towards the driver's side vent or door mirror. You will recognize the braided cable. Use that to orient yourself. There is a nut that holds it in place way up there, and of course the blue wire connector. It's a 10mm (duh).

Now, you can also gain a viewport if you pull the driver's side vent stack piece off the dash (the silver curved piece with the vent in it). Just pull gently away from the dash at the top and bottom and it will come off.

So now just do what you can from underneath and come up and peek through your new dash hole when you need to orient yourself.

Took about 15 minutes to replace. I'm sure much easier and faster than ripping the dash apart as in the video above.

FYI my original and replacement resistors were exactly the same rating: 193.6 mOhm.

 

Your post saved me a lot of worry. I was going to give up on replacing the resistor especially after a stressful day of pulling the accumulator out. I did end up replacing the resistor just like you described in less than 5 minutes.